The present invention generally relates to a gas supply system that can supply a material gas at different flow rates from a plurality of gas supply ports formed in a device manufacturing chamber, such as a semiconductor manufacturing chamber or a liquid crystal display manufacturing chamber.
Recently, due to an increase in size of a wafer, a semiconductor manufacturing chamber supplied with a material gas from not only one supply port but from a plurality of supply ports at the same time has been developed. However, even if the material gas is supplied at an equal flow rate from each gas supply port of such a chamber, gas concentration may vary on the wafer. Therefore, to equalize the gas concentration on the wafer, the flow rate of the material gas to be supplied from each of the gas supply ports may be varied.
Incidentally, the material gas is a mixture of a plurality of component gases at a predetermined proportion, the plurality of component gases being, for example a major component gas (e.g., O2, Ar and N2) and a minor component gas.
In a semiconductor material gas supply system for supplying the material gas to the semiconductor manufacturing chamber as above, the flow rate is controlled by providing a flow rate control device in each of the component gas flow passages where the component gases are supplied, respectively, and the component gas flow passages are merged into a single passage (a material gas flow passage) so as to combine the component gases to form a material gas therein.
However, in practice, a finely mixed state where the component gases spread uniformly in the main passage is not always achieved. For example, the minor component gas may not mix with the major component gas and, as shown in FIG. 8, a large amount of the minor component gas may flow along an inner wall surface of the material gas flow passage.
In this case, when the material gas flow passage is bifurcated and the material gas is led to each of the gas supply ports of the chamber, one or more of the bifurcated passages may include an excessive amount of the minor component gas, a concentration ratio of the component gases may be different in each bifurcated passage, and as a result, a negative effect may be caused in the manufacturing of a semiconductor.
In order to avoid the above situation, simply, the plurality of component gas flow passages, where one of the component gases flow, may be connected to the gas supply ports, respectively, so that each flow rate in the component gas flow passage is controlled. However, such a structure requires a set of a flow rate control mechanism (a valve), an upstream pressure sensor, a fluid resistance element, and a downstream pressure sensor, for each component gas flow passage, which may lead to a large increase in size and cost.